1990 Toyota Celica GTS. Idle races too high

(which engine. ?????)_
as always check all fuses. and scan the ECU for DTCs. first.
there is no need to fix OBD2 cars like 1980 cars (hard rows to hoe)
it can be 2 problems this......
lets fix the easy one first. idle. (and hope for moving issues to fix for free) it idle car is parked, so is 100% safe tests. (not moving)

so it surges at idle.
questions.?
1: hot or cold or both.?
2: low extreme RPM and high at idle.
400 to 800 RPM? surge.
1000 to 2000. what? numbers tell the tale.

first off, idle is the last thing to work right on any engine.

there are many ways to find what is wrong.
fix idle surge way.
i make sure that the engine holds closed LOOP status.
hot idle, if not , i fix that first.
keep in mind if not in closes loop and lean
all lean engine surge and guess what the ISC will add to the surge
because idle is way too slow, so the ECU open the ISC wider
and wider and its still too slow, so the ECU resets the ISC
this cause a worst hunt (surge)
the ECU adjust spark time and the ISC to get 800 rpm. (spec. look up yours)
so say , i see closed loop failed, OBD2 scan page 1
i look at the O2 sensor an its stuck lean.
if stuck lean and it really is (o2 bad?) then its lean and it will surge
.
examples.
1: i find 02 sensor bad, (only effects idle and light steady cruise)
2: i find fuel pressure at 15PSI , hopeless low .
3: i find all injectors clogged. and lean.
4: with MAF EFI, ( i find maf reading too low, (dirty) causing lean.
5: if MAP car, i find the MAP stuck hard high vacuum causing lean.
not knowing what engine you have or the idle hot surge range,
i can not go farther.

the driving bog tells me,
1: scan the ecu ,get DTCs; do that first.
2: clean MAF if car has one, ask how..
3: check fuel pressure.


my guess is engine is lean. and starving for fuel all the time.
cept WOT.

MAF cars starve for fuel if there are any vacuum leaks.
MAP cars do opposite, they race fast with 100% full power.
MAF is air density EFI
MAP is speed density EFI.
apples and oranges diffr. so what engine.

sounds like you may have a vacuum leak. any air entering engine not passing through the throttle body will cause engine to race. a whistling sound is sometimes a sign of vacuum leak but not always audible. propane is the recommended method finding leak but I find this unreliable. spraying carb cleaner around suspect areas and listening for a rpm change is more successful. just remember carb cleaner is extremely flammable and caution must be used.

Try cleaning the throttle body and check the gap on all the spark plugs also all electrical sensor plugs and battery terminals this could be related to engine temperature also if to hot rpms stay up longer to cool off but maybe your idle air control valve is bad when did it start?

If well maintained and with regular service this engine can last up to 150,000 miles. Remember, this means changing all fluids regularly, changing the hoses and belts regularly and just keeping the engine in tip top condition. No racing, no over revving, etc.

If you replaced the whole engine wire harness,make sure all connectors are hooked up , if they ok ,check MAP sensor and temp. sensor .it might be your problem.If possible swap them with known good used ones, or just try to disconnect it and see if it runs any better.

Here are the most common causes of idle surge, stalls at stops, slow idle speed, erratic idle speed, rough idle and engine hesitation (and other problems), it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake

Vacuum leak or bad IAC or Map sensor.

Check the idling if it is erratic. It may be a dirty fast idle control valve or leaking vacuum hoses.

it may be one of the water temp. sensors at the thermostat housing.

also check the plug, wires,distributer cap and rotor.

good luck

22re owner

please change the idling swicth control valve unit and your problems will be gone for good!!